WEBVTT FIREFIGHTER WAS THRILLED TO WELCOME HIM AS ONE OF THEIR OWN. REPORTER: >> THIS IS A SPECIAL CALL TO DUTY. >> A FIREFIGHTER IN THE FRONT OF MY HOUSE. LIKE, WHAT? REPORTER: HE HAS MASSIVE SEIZURES AND STOPPED BREATHING. HE HAS TERMINAL BRAIN STEM CANCER. TODAY A GOOD ADRENALINE RUSH. >> THIS IS RILEY. >> THE FIRST THIRD-GRADER SWORN IN AS A CHELSEA FIREFIGHTER. >> I CAN' IMAGINE WHAT HE AND HIS FAMILY ARE GOING THROUGH. IT PUTS THINGS IN PERSPECTIVE FOR YOU. REPORTER: THE JOY OF THIS. THE OLDEST OF FO SIBLINGS, -- >> I JUST WANT TO SPRAY THEM. REPORTER: HE COMPARES IT TO HIS REGULAR DAY. TOYS ON THE ENGINE WORTHY OF TAKING HOME. >> MAYBE THEY WILL GIVE YOU ONE. >> I'M A VERY NICE BOY. REPORTER: HIS FAMILY APPRECIATED TODAY. THEY WORRY ABOUT HIS EVERY TOMORROW. >> YOU NOTICE THE PEOPLE WALKING BY TREASURING EVERY MEMORY WITH HIM. >> YOU ARE LIKE PART OF MY FAMILY NOW. THIS IS THE MOST FUN I HAVE EVER HAD.